The overall goal of this proposal is to establish the regulation and function of sulfotransferase (SULT) 4A1 in the developing zebrafish (Danio rerio) embryo/larval model system. SULT4A1 is an orphan enzyme that has been included in the cytosolic SULT gene family based upon its structural homology. SULT4A1 protein is selectively expressed in neurons in the vertebrates examined. The function of SULT4A1 in the nervous system is of interest since the protein is greater than 98.5% identical in amino acid sequence in mammals and almost 90% identical in vertebrate species, including zebrafish. In humans, the SULT4A1 gene has been identified as a susceptibility gene for the occurrence of schizophrenia based on both transmission disequilibrium studies and its association with psychopathology. To date, no convincing evidence as to its substrate selectivity or activity has been identified for th enzyme in any species or following cell or bacterial expression and purification. The high homology of zebrafish SULT4A1 to the enzyme in other vertebrates provides a valuable model system for the examination of its developmental regulation and function. The zebrafish embryo/larval model allows for the analysis of SULT4A1 tissue specific expression, temporal regulation, enzymatic activity and effects of down-regulation of expression using egg injection of selective inhibitory morpholino oligonucleotides. SULT4A1 mRNA and protein are expressed in 4-day old zebrafish larvae demonstrating the potential to analyze its regulation during embryogenesis and larval development. A more complete comprehension of SULT4A1 function and activity in zebrafish, as elaborated by the following specific aims, will provide valuable insights into its role in human neurobiology. Aim 1 To analyze the tissue-specific developmental expression of SULT4A1 in the zebrafish embryo/larval model system. Aim 2 To investigate the morphological and physiological effects of selective down-regulation of SULT4A1 expression during zebrafish embryonic development. Aim 3 To investigate the activity and substrate selectivity of SULT4A1 using the zebrafish embryo/larval developmental system.